The Adeptus Custodes are the Emperor's praetorian guard, the defenders of Terra and watchers over the Golden Throne. But when a threat arises, they and their Sisters of Silence allies may find themselves pressed almost beyond endurance…

As the Emperor marshals his armies to reclaim the galaxy for the glory of mankind, one by one his Space Marine Legions are reunited with their missing primarchs. The XVIII Legion are still waiting to find their true identity, unaware their own lord has been found. In the Taras Division, legionaries face annihilation as they take a last, desperate stand against a monstrous ork invasion. Meanwhile, on Nocturne, Vulkan has raised and trained a new force of warriors. Now it is the time for him to lead his sons into battle. Now it is the time for him to truly don the mantle of primarch, not only to save one half of his Legion, but forge a new, indivisible whole.

Trapped behind enemy lines during the invasion of Rynn's World, Sergeant Galleas and his squad must rally the human survivors of the greenskin attack and teach them to fight back, if any of them are to survive.

The Casus Belli, an Imperator Titan that has defended the Imperium for ten millennia, marches to war at the head of an army of Adeptus Mechanicus – but will treachery end the god-machine's long legacy of glory?